The claimed invention relates to a device in a guide bar for a chain saw. The guide bar comprises at least two layers that are bounded together by an adhesive material.
Chain saws and other hand held tools have been under a high level of development during the last years. Great efforts have been done to improve the performance and the ergonomic features for the tools.
New materials and methods for manufacturing the different components have made it possible to reduce the weight of the tools. The tools are also stronger and more reliable which improves the working conditions for the operator considerably. Great achievements have been done with the machinery and casing, while the development of the guide bar have been struggling with several problems. The biggest problem is that since all new solutions for reducing the weight of the guide bar has ended in that the performance of the guide bar is deteriorated because of a reduced torsional and/or bending stiffness.
Guide bars normally comprises three layers. Layer one and three constitutes the outside of the guide bar. These two layers are normally made of the same material that most often is some kind of steel. Between layer one and three is layer two placed as an intermediate layer. This layer could be made of another material than layer one and three. The intermediate layer has a smaller length and width than layer one and three that are identically shaped so that a groove around the entire edge of the guide bar is defined between layer one and three. The saw chain is sliding in this groove.
Different types of saw chains require different grooves so the depth and the width of the groove are selected in order to meet the requirements. The width of the groove is changed by the thickness of the intermediate layer and the depth of the groove is related to the length and width of the intermediate layer.
The three layers are attached to each other by welding, normally spot welding or pressure welding. To make sure that the welding achieves enough strength and that no welding spark end up in the groove for the saw chain is the centre of the welding spot placed about 6 millimeters inside the edge of the intermediate layer, which is the same as the bottom surface of the groove. The distance from the centre of the welding spot to the edges of the groove is consequently 6 millimeters plus the depth of the groove. Because of this distance will the sides of the groove bend outwards when the saw chain is exposed to high load during use. The movements in the sides of the groove will make the saw chain move because of to much play in the groove. The movements in the saw chain are not good for the performance of the saw and will also increase the wear on both the guide bar and the saw chain.
The weight of the guide bar is an important parameter in order to facilitate and increase the efficiency of the work for the operator. Several different types of guide bars with an intermediate layer provided with holes of different sizes in order to reduce the weight of the tool are already known. A guide bar of this type is for example described in patent document DE4219956A1. These guide bars have a lower weight but the torsional and bending stiffness are reduced, which is bad for the performance of the guide bar.
Another alternative in order to reduce the weight of the guide bar is to use an intermediate layer in a material with low density like for example aluminium or a plastic material. These types of guide bars are described in patent document U.S. Pat. No. 4,693,007A. An intermediate layer in aluminium or a plastic material reduces the weight of the guide bar but the manufacturing of the guide bar get more complicated since the material in the intermediate layer not is suitable for welding. To solve this problem is the intermediate layer provided with recesses of a material suitable for welding placed where the welding spots will be placed. This type of guide bars is expensive to manufacture.
All the described types of guide bars are complicated which means that they are expensive to manufacture. The guide bars also have the drawback that the holes and the use of lighter materials to reduce the weight decreases torsional and bending stiffness of the guide bar which makes these solutions not satisfying.
There are also guide bars with recesses of a lighter material like aluminium or plastic in the outer layers, see for example U.S. Pat. No. 4,837,934A. However, this solution is also complicated to manufacture and the result is a guide bar with reduced torsional and bending stiffness. This solution is therefore not a good alternative to get a lighter guide bar.
All solutions to reduce the weight of the guide bar has resulted in a more complicated manufacturing process which makes the guide bars costly without improving the performance of the guide bar.
A new type of guide bars has therefore been developed where an adhesive material bound the layers. The guide bar normally comprises three layers. Layer one and three constitutes the outer sides of the guide bar. Between theses two layers is an intermediate layer of a material with lower density placed to reduce the weight of the guide bar. An adhesive material cured under pressure at a high temperature so that the bounding gets maximum strength bound the tree layers.
Guide bars of the described new type have higher torsional and bending stiffness compared to known guide bars. The guide bar also has lower weigh than known guide bars. The higher stiffness and lower weight improves the performance of the chain saw and reduces the loads that the operator is exposed to.
Guide bars normally comprises three different layers. Each guide bar will consequently comprise two layers of adhesive material to bind the different layers together. If the adhesive material is applied between the flat surfaces that will be bounded together is it difficult to get a layer of adhesive material with a constant and optimal thickness. If the thickness of the layer of adhesive materials not is the optional one will the strength of the bounding be effected in a negative way. Another problem is that the width of the groove that is extending around the guide bar will alternate and therefore not meet the requirements from the saw chain. This may cause additional sideways movements in the saw chain if the width is to big, or that the saw chain gets caught in the groove if the width is too small. Increasing movements sideways and friction also increases the wear on the guide bar and the saw chain.
The claimed invention solves the described problem by providing one of the surfaces that will be in contact with each other with protruding parts with a predetermined heights placed on the surface. The height of the protruding parts generates a slot between the surfaces. The thickness of this slot equals the height of the protruding parts and the thickness of the adhesive layer is therefor controlled by the height of the protruding parts so that the thickness of the adhesive layer is optimal for maximum strength of the bounding.
If the protruding parts are placed on both sides of the intermediate layer is it only necessary to provide the intermediate layer with protruding parts. The protruding parts are manufactured in different ways depending on the material in the intermediate layer. If the intermediate layer is made of aluminium is hobbing or embossing a suitable method for manufacturing while other materials requires methods like for example casting in a mould.
In order not to reduce the strength of the sides of the groove are the protruding parts placed so that they not will effect the bounding in the area close to the bottom of the groove. This means that the protruding parts are placed at a distance from the edge of the intermediate layer.
The protruding parts could be shaped in different ways. If the curing of the adhesive material is to take place under a high pressure is the area of the protruding parts preferably larger so that the layer that will align the protruding parts will rest in a stable way. One preferred embodiment of the protruding parts is a circular shape or another shape were the surface of the protruding part that will align the other layer is placed around the periphery of the geometrically shape. This embodiment will provide good support for the other layer without reducing the area where the adhesive is acting since adhesive may be applied inside the geometrical shape.
There is a big risk that layers bounded by an adhesive material that is cured under a high temperature and pressure will slip in relation to each other before the adhesive is cured. This problem is solved by applying a small amount of a quick-acting adhesive so that the layers are secured to each other and prevented from slipping during the curing of the adhesive. The adhesive material is applied in the predetermined pattern on the surface of the layer before the quick-acting adhesive finally is applied at some small areas on the surface of the layer. These small areas are preferably on top of the protruding parts. The layers are then put together and held in the right position in relation to each other by the quick-acting adhesive until the adhesive is cured at high temperature and pressure so that the bounding achieves the maximum strength.
A less complicated type of guide bar serves as a second embodiment of the claimed invention. This guide bar comprises only two layers. The edge that surrounds the layer is bent so that a groove is created when the two layers are put together. An adhesive material bound the layers. The described solution for controlling the thickness of the layer of adhesive material is adaptable also for this type of guide bar. One of the layers is provided with protruding parts while the surface of the other layer is flat so that a slot with constant width are generated between the layers when the layers are put together.